More colors filled in. Just ignore the dots in the top-left corner. I made those just to remember which colors I had used.

Fill the white in the eye with a light gray with some blue in it. I choose a green iris color. You can of course select another color. You can actually get away with pretty 'wild' eye colors. I've read somewhere that like with fingerprints no eyes look
the exact same. Some have very bright eyes, looking almost spookey if you ask me. I find dark eyes more friendly and warm, but thats just me.

Some people have eyes with an almost awkward color, a mix between blue and green. But then you see them in a different light and now they look green and yellow. My advice is to go for an "established" eye color combination in a painting, unless you want that extra attention to the eyes though.

I paint my eyes the same way each time; You have a round and black pupil (the pupil can vary a lot in size, depending on the lightning situation or drug abuse :-)) The iris is the round, colored area around the pupil. On most people the iris has a dark edge both towards the pupil and the eyeball. More ramblings on the iris later in this lesson!

The Iris and the pupil suggested

Start suggesting the depths in the image. The top/center of the eyelid is rendered light because it 'stands out' in the image. The same goes for the area above the eyelid and below the eye brow. As the opposite, the left part of the skin area is painted darker to illustrate that the skin curves back. The area around the eyes is particularly skinful.

You have probably seen drawings/photographs of the human skull and noticed that the eyesockets are much bigger than our eyes. With age, human skin looses some of its firmness and develop wrinkles and creases in the area below the eyes (maybe gravity plays an effect too, I don't know :))

The skin above the eyelid is affected too if not exactly creasing, it starts sagging and can eventually cover the eyelid completely. This probably isn't new to anyone, but I want to illustrate that such should be remembered when drawing people. Age is a part of our identity...